This invention relates to a height adjustment device, particularly for the seat back portion and arm-rests in office chairs.
Office chairs are known comprising a spoke-type base with feet or wheels, a column mounted on said base and provided with a gas piston for adjusting the height of the sitting plane from the floor, and a support plate supported by said column, and on which the seating portion rests.
The back-rest support bracket and the arm-rest support brackets are generally connected to the seating portion support plate.
IT-B-1.288.164, filed in the name of the present applicant, describes a device for adjusting the seat back portion comprising a guide element rigid with the support plate of the seating portion, a back-rest support slide engagable with said guide element and slidable along it, and elastic means selectively engagable with a toothed portion to ensure the stability of the position of the slide relative to the guide.
This device has however proved to be susceptible to improvement both with regard to the ease finding the correct position of the arm-rest and/or seat back portion relative to the seating portion, and with regard to avoiding undesirable slippage of the arm-rest or seat back portion relative to the seating portion if the chair is lifted via these parts.
This improvement is attained according to the invention by a height adjustment device, in particular for seat back portions and arm-rests in office chairs, as claimed in claim 1.